In its simplest form, feed takes place via ports. In theory, at any given speed, it ought to produce twice the power of a four-stroke engine, since the number of drive strokes is doubled.
The power obtained in reality is very much less than the theoretical power, because cold gases are lost via the exhaust, particularly at low speeds.
In controlled-ignition engines, which are fed with a preformed mixture, mixture is lost to the detriment of consumption and pollution.
The design of these engines has remained very largely empirical. Nevertheless, it is known that losses to the exhaust come from:
suction by the exhaust into the conically-shaped reduced pressure zone in the combustion chamber due to the gas flows therein; and
direct flow of admission content into the exhaust, thereby setting up both said exhaust pressure reduction and the admission pressure.
Proposals have been made to remedy this direct suction of admitted mixture, at least in part, by using a solid deflector, for example a projecting portion of the piston, in order to constitute an obstacle to such direct flow. Proposals have also been made to provide pneumatic deflection of the admitted flow of mixture, by establishing an admission flow directed away from the exhaust.
An effective solution of the problem of exhaust losses lies in direct fuel injection. Unfortunately, this technically acceptable feed device is economically unusable because it is much more expensive than the engine itself. It is therefore necessary to continue to use engines with a mixture that is pre-formed prior to admission into the cylinder.
In an earlier patent, the Applicant has proposed a combustion chamber including multiple admission, i.e. for admitting both a mixture formed prior to admission via an inlet in the opposite side of the cylinder to the exhaust outlet and a flow of air containing no fuel which is admitted via two symmetrical ports directed towards the wall furthest from the exhaust port so as to counterbalance the tendency of the mixture to move diametrically across the combustion chamber. These dispositions are used in combination with a cavity in the cylinder head for accumulating the mixture and for obtaining uniform combustion at top dead center.
In a recent study, a Japanese institute has shown the important role of such a cavity in the cylinder head in reducing losses of mixture flow to the exhaust. The study relates to an engine having single admission of fuel mixture.
The present invention relates to measures stemming from the above-mentioned study and from the Applicant's earlier patent, so as to delay the flow of mixture in the combustion chamber relative to the flow of the air contained in said chamber, thereby tending to avoid loosing mixture via the exhaust. The cavity constitutes a retention space because it reflects the air flow thereby setting up a flow in the opposite direction to the flow of mixture inside the cavity, thereby momentarily stopping said mixture flow at the top of the chamber.